Injection molding is a major plastic part process. The mold is a two-section tool that has a hollow cavity in the center. The hollow form is filled with plastic to make the part. The injection molding process has as its general steps closing of the mold, application of clamping force, injection of plastic, curing of plastic, opening of the mold, and removal of the part. This process is then repeated. The mold halves close and a clamp force is applied to keep the two halves closed to resist the injection pressure inside the mold. The plastic flows in the hollow form to make the part.
Injection compression molding is similar to injection molding, with the major difference being that the plastic is injected without clamping pressure applied on the mold. The plastic is injected while the mold is not fully closed. During the final phase of the injection, the mold is closed and clamping force is applied to compress the plastic to make the shape. Thus, injection compression molding requires less clamping force because force is not needed to resist the pressure in the injection phase. The general steps of this process include injection of plastic in a slightly open mold, closing of the mold, curing of the plastic, opening of the mold, and ejection of the part.
Injection molding can be used to make complex parts, but its disadvantage is that the clamping force increases with the complexity and size of the part. Injection compression molding has the advantage of reduction in clamping force, a reduction of approximately 50-70%, but its disadvantage is that the part is smooth in shape.
It is seen then that there exists a need for a new process which combines certain advantages of both injection molding and injection compression molding, but eliminates certain disadvantages of each process.